Method and apparatus for digesting cellulose bearing material



METHOD AND APPARATUS FOR DIGESTING CELLULOSE BEARING MATERIAL Feb. 12; 1935'. J. J. .DE LA Roz'A, SR

Filed Sept. 21, 1933 2 Sheets-Sheet 1 ATTOZNEY Feb. 12, 1935'. 4. J. DEL A ROZA, SR 4 V METHOD AND APPARATUS FOR DIGES'IEING CELLULOSE BEARING MATERIAL ZSheets-Sheet 2 Filed Sept. 21, 1933' I JIMEA Z 'A'ITORNEY Patented Feb. 12, 1935 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR DIGESTING CELLULOSE BEARING MATERIAL Joaquin Julio de la Roza, Sr., New York, N. Y.,

assignor to de la Roza Corporation, Wilmington, Del., a corporation of Delaware Application September 21, 1933, Serial No. 690,406

24 Claims.

One object of my invention is to provide an.

apparatus and a method for the continuous digesting of cellulose bearing material in order to achieve greater economy, a higher yield, and a superior quality of product.

Another object of my invention is to provide a process of digesting cellulose bearing material in which the material to be digested is compacted to form of itself a cork or plug capable of withstanding the pressure existing within the digesting zone.

Another object of my invention is to provide a method for digesting cellulose bearing material in which a high volumetric density may be employed in order to increase the efliciency and output of the process and the quality of the product.

Another object is to provide means for moving the highly compacted material forward as the digestion proceeds.

A further object of my invention is to provide a method for reducing the time of digestion.

Still another object of my invention is to provide a method of digesting in which a predetermined level is maintained within the digesting zone in order to produce uniform digestion throughout the digesting material.

Another object of my-invention is to provide a method of digesting cellulose bearing material in which the rate of feeding boththe cellulose bearing material and the digesting liquor, and the rate of withdrawing the digesting material are controlled by the level of the digesting material within the digesting zone.

Other and further objects of my invention will appear from the following description.

In the accompanying drawings which form part of the instant specification and are to be read in conjunction therewith, and in which like reference numerals are used to indicate like parts in thevarious views;

Figure 1 is a diagrammatic plan view of an apparatus capable of carrying out the process of my invention.

Figure 2 is a diagrammatic elevation of the apparatus shown in Figure 1.

Figure 3 is a diagrammatic sectional elevation of the apparatus shown in Figure 1 cmbodyin'g one form of my invention and capable of carrying out my process.

In general, my invention contemplates the provision of a substantially horizontally inclined elongated digesting vessel having a cross sectional area not less than one and one quarter and not more than six times the cross sectional area of the restricted inlet leading to the vessel.

converges and then diverges in the direction of the material feed. A reciprocating pistonal plunger is adapted to force the material being fed through the restricted inlet which, by vir- The restricted inlet is tapered and first tue of its taper, compresses or compacts the material being fed. I contemplate thoroughly impregnating the fibrous or cellulose bearing material with a solution of digesting chemical before the material'is compacted so that the pores of the material will be thoroughly satu- The column of material being fedme to eliminate corks to mechanically restrain, 3'

such as screws or the like. The digesting vessel itself is provided with a steam or vapor dome at the top thereof and communicating therewith. The digesting ,vessel is positioned substantially horizontally, and slightly higher at the inlet end than at the outlet end in order to permit. a downward flow of the material. The vessel-is proportioned so that it is substantially thirty times or more as long as its" diameter. At'suitable places along the shell I provide expansion means for permitting longitudinal expansion of the vessel. The steam or vapor dome accommodates slight changes in thevolume of the liquid, while at the same time permitting the digesting vessel proper to be completely filled, with material at high density. This is of importance because the failure to completely fill the digesting vessel to high density permits material which has not become thoroughly impregnated with digesting liquor to float on the surface of the liquid which would be formedif the vessel were not completely filled. It will be observed, by impregnating the material being fed with digesting liquor before compacting the same that I tend to obviate the difficulty of feeding dry, light material to the digesting zone, which material will have a tendency to float.

Within the digesting vessel I provide in suitable bearings, a perforated cylinder provided with means to rotate the same. The portion of the cylinder nearest the inlet for the material to be digested is tapered and given the shape of a frustrum of a cone. The cylinder is constantly rotated to insure a thorough mingling of the material to be digested with the digesting liquor, and to move the mass forward. In order to maintain the temperature within the digesting zone, which I prefer to be a maximum of 173 C. for the alkaline process, and 150 C. for the acid process, I provide means for continuously withdrawing a portion of the liquor from near the outlet end of the digesting vessel, heating the withdrawn liquor and returning it to the digestor, preferably at a point within the first third of the length of the vessel. I feed the digesting liquor into the digesting vessel at a point in the vicinity of the conical portion of the rotating cylinder. In order to insure that the fresh liquor is sumciently heated, I provide means for introducing into the fresh incoming liquor a portion of the heated, recycled liquor. I prefer to sufiiciently heat the recycled liquor so that the temperature of the resulting mixture entering the digesting zone will be about 110 C. for the acid process or about 140 C. for the alkaline process. In order to maintain the proper digesting temperature, I provide a temperature control means for governing the amount of heat passing through the heat exchanger.

In this connection, attention is invited to the fact that it will be possible in the alkaline process to introduce a mixture of fresh digesting chemical solution and partly exhausted circulating chemical solution, unaffected by contact with the atmosphere as would be the case in the usual black liquor now employed. The fresh digesting chemical will be diluted in such proportion that its concentration of alkali will be but a fraction of its full and maximum concentration as produced by the recovery system, thus inhibiting mercerization of the cellulose bearing material and enabling the resulting temperature of the mixture being introduced into the digesting vessel to be controlled so that it may be kept within desired limits. I am thus enabled to obtain complete impregnation of the cellulose bearing material by hot digesting liquor before full digesting pressure and temperature are attained. If the fresh chemical solution is heated to below C. it may be brought up to the proper temperature by admixing therewith a suflicient quantity of heated circulating liquor.

More particularly referring now to the drawings, a digester shell 1 may be of any suitable construction and provided at intervals along its length with expansion and sealing joints 2. Near the inlet end of the shell 1 and communicating therewith I provide a vapor or steam dome-3 fitted with a relief valve 4. Mounted within the shell 1, in suitable bearings 5, I provide a cylinder 6 provided at its inlet end with a conical portion 7. The cylinder is provided with means for rotating the same. In the modification shown in the drawings, a ring gear 8 is secured to the cylinder as shown and adapted to be driven from electrical motor 9 which drives pinion 10 through reduction gears 11. If desired, the cylinder 6 may be driven from a number of points. The cylinder is provided at suitably spaced points along its length with perforations 12. These perforations are of such size as to retain the fibrous material within the cylinder, while permitting the digesting liquor to pass through for recirculation, as will be hereinafter more fully described. The perforations near the inlet end areabout one fourth inch in diameter, while those near the outer end are one sixteenth inch in diameter. The size of the perforations may be varied as desired. The conical portion 7 of the cylinder 6 bears against the inlet member 14. It will be observed that the inlet member 14 communicates with a hopper 15 and that portion of the inlet passage 16 extending from the hopper 15 toward the inlet end of the digester converges to form a restricted throat 1'7. From the throat 17 to the digesting vessel, that portion of the inlet passage 18 diverges. In order to refer to this progressive converging and then diverging cross sectional area of the inlet passage, the inlet passage will be referred to as a convergingdiverging passageway. A conveyor belt 19 is adapted to feed cellulose bearing material, which may be such woods as spruce, pine, fir, oak, hemlock, poplar, or others in combination or alone, or fibrous grasses including sugar cane fibre, bagasse, corn stalk, bamboo, straw, cotton stalks, fiax stalks, jute, hemp, sisal, manila, and the like. The cellulose bearing material is comminuted and fed to the conveying mechanism which is driven by any suitable means as for example motor 20. The throat of the hopper 15 is provided with a jacket 21 provided with openings 22. A chemical solution tank 23 is placed in communication with the jacket 21 by means of pipe 24. A pump 25 driven by a suitable motor 26 is adapted to pump chemical solution from tank 23 to jacket 21 for spraying through the perforations 22 as can readily be seen by reference to Figure 3. the fibrous material will become impregnated with chemical solution before passing into the inlet passage. A reciprocating plunger 2'7 driven by any suitable means is adapted to ram or compact the chemically impregnated cellulose bearing material through the converging portion 16 of the inlet passage. The packing of the chemically impregnated cellulose bearing material will increase its density at the same time forcing chemical solution through the pores of fibrous material. The column of compressed material will be at least as dense as a solid piece of wood, while possessing a tendency to spring apart. The density to which the material is compressed will be in the neighborhood of 35 pounds of fibrous material per cubic foot. This highly compressed column of fibrous material being forced through the restricted portion 17 into the diverging portion '18 will form an advancing, continuous cork or plug, of a density of at least 20- pounds per cubic foot of dry fibrous material, adapted to withstand the pressure existing within the digesting zone. As the compressed material emerges from the inlet passage 14 into the conical portion 1 of the cylinder 6 in the digesting zone, it will expand to a density of 20 to 18 pounds or lessper cubic It will be observed that foot of dry fibrous material. Itwill be seen that my method of feeding the fibrous material to the digesting zone makes for a high density of fibrous material within the digesting zone. Fresh digesting liquor from any suitable source passes through pipe 30 to pump 31, which is driven by any suitable means, as for examzone in the region of the conicalportion of the cylinder; s

.From any suitable point in the digesting zone I withdraw a portion of the digesting liquor through line 35, which is controlled by valve 36, and pump the same b g means of pump 3'1 through line 38 to a'heat exchanger 39. Any suitable heating medium, as for example steam, passes through line 40, through valve 41, through the heat exchanger 39 in heat exchange with the withdrawn liquor, and passing out through-line 42. The 'rate of heat exchange is such that in the alkaline process the recycle liquor passing through the heat exchanger will be heated to about 173 -C. while in the acid process it will be heated to about 150 C. The heated recycle liquor will leave the heat exchanger through line 43 and pass through line 44 through valve 45 into the digesting zone. The point of introduction of the recycled, heated liquor is preferable within the first third of the length of the digesting zone.

A bleeder line 46 controlled by valve 47 is adapted to bypass a portion of the heated recycle liquor into line 33 for admixing with the fresh incoming liquor. By controlling valve 4'7, I am enabled to heat the incoming liquor to about 140" C. in the alkaline process or C. in the acid process. It will be observed that I do not introduce the digesting liquor to the cellulose bearing material in the digesting zone at the full or maximum digesting temperature. The maximum temperature is not reached until the point of inlet of the heated recycle liquor through line 44. By this method, the cellulose bearing material will become properly penetrated before the full digesting temperature is reached. This prevents charring and makes for a uniform product. The velocity of the recycling will be relatively low so as not to interfere with the forward movement of the digesting material through the digesting zones The rotation of the inner cylinder 12 will maintain a smooth homogeneous mixture, making for a uniform product and, at the same timefpermitting the high density of fibrous material to be employed.

It will be further observed that my recycling system enables me to eliminate the use of undesirable black liquor to make up a diluted mass capable of being handled, thus preventing undue liquor dilution. It follows, furthermore, that the elimination ofblack liquor in the alkaline process will prevent the fixing in the finished pulp of coloring matters, which in turn lowers the amount of bleaching required, resulting not only in a high yield but in a product of better quality.

It willbe seen, further, that my method of recycling will reduce almost by one half, the quantity of liquor which it is necessary to heat or otherwise handle in chemical recovery such as is the case in the digesting systems of the prior art.

ing electromagnet 71 controlling valve 41.

If desired, the liquor for recycling may be withdrawn from the lower portion of the steam or vapor dome 3 or any other suitable pointv in the process. After the cellulose material has been cooked by passage through the digesting zone, which as pointed out above, may be somewhat inclined to facilitate the passage of the digesting material therethrough, it is deflected downwardly by the end wall 50 of the digester and passed into conduit 51 to a volumetric valve 52 which-is mounted on shaft 53 adapted to be rotated by motor 54. The valve 52 will be driven at a speed consistent with the grade of pulp being produced. If the pulp is under cooked. the valve may be slowed down by adjusting motor ,54'. If it is over cooked, it may be stepped'up.

The volumetric discharge valve admits into a downwardly extending passageway 54 which discharges tangentially of cylindrical baflle 55 which extends into the blow tank 56. The blow tank acts as a .gas, steam and vapor separator, the vapors and gases passing upwardly through the passage 57, through condenser 58. The bottom of the blow tank 56 is fitted with an inlet pipe 59 into which additional liquor may be added to dilute the digested stock in order to enable it to flow out of pipe 60 and be handled by pump 61 so that it may pass through line 62 in the diluted condition, where it is handled by washersv in the usual manner known to the art. An agitator 63,- driven by a suitable motor 54 insures that the digested mass is kept thoroughly agitated to enable its being handled in a sufiiciently diluted form enabling it to flow. Within the first third of the length of the shell as for example at 3 I position a thermocouple '70 adapted to make and break a circuit operat- It will be observed that, by this arrangement, if the temperature within the digesting zone falls below a predetermined point, the valve 41 will be opened further to admit a greater supply of heating medium to the heat exchanger and, if the temperature be above a predetermined point, the arrangement is such that the valve 41 will tend to close, thus reducing the supply of heat furnished to the circulating recycle liquor. The level of the digesting liquor will-rise within the dome 3 to actuate float 72 which controls, through any suitable arrangement, rheostats 73 and '74. s

It is to be understood, of course, that the showing is merelydiagrammatic and is well understood by those in the art. As the level within the dome 3 rises to actuate float 72, the arrangement is such that rheostat or control member '74 is actuated to slow up motors 32, 26, and 20. It will be observed that this will decrease the input of fresh chemical solution by slowing down motor 32. The amountof fibrous material being fed will be decreased due to the fact that motor 20 is slowed, and motor 26 will effect a corresponding decrease of the impregnating solution for the dry fibrous material. At the same time, upward movement of the float will serve to operate control -73 in the opposite direction to increase the speed of motor 54' which will rotate the volumetric valve faster so that the material will be withdrawn more'rapidly; If the level within the vapor dome 3 should fall below a predetermined point, the

opposite action will occur and the material and I the digesting liquor will be fed more rapidly and the volumetric discharge valve will be slowed to lower the rate of withdrawal.

It is believed that the operation of the process will be clear from the foregoing description.

It will be seen that I have accomplished the objects of my invention. I am enabled to continuously treat cellulose bearing material at a very high density to produce a uniform product high in quality with a maximum of economy. I am enabled to charge cellulose bearing material in the form of a. compressed column adapted to act as a cork to withstand the pressure existing in the digesting zone. By impregnating the cellulose material before it is compressed into the form of a compacted column I disseminate digesting chemical through the fibrous material before it enters the digesting zone, thus aiding in digestion and increasing the quality of the product. By rotating the shell I insure forward progress of the contents from the inlet to the outlet, and uniformly agitated digestion. My process conserves heat in the entire system and my apparatus gives a very close heat control, resulting in the formation of a uniform product. By eliminating the use of black liquor I obtain a pulp of good color, thus reducing the amount of bleaching required.

It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention, what I claim is:

l. A digesting apparatus including in combination a digesting chamber, an elongated cylinder positioned within said chamber, means for rotating said cylinder, means for introducing the material to be digested into said cylinder and means for withdrawing digested material from said cylinder.

2. A digesting apparatus as in claim 1 wherein said cylinder is provided with perforations.

3. A digesting apparatus as in claim 1 wherein said cylinder is provided with a tapered portion in the vicinity of its inlet end.

4. A digesting apparatus comprising in combination-an elongated substantially horizontal vessel formed with an enlarged chamber communicating with the upper portion thereof, means for introducing material to be digested into said vessel, and means responsive to the level of the material in said enlarged chamber for controlling said material introducing means.

5. A digesting apparatus comprising in combination an elongated substantially horizontal vessel formed with an enlarged chamber communicating with the upper portion thereof, means for withdrawing digested material from said vessel, and means responsive to the level of the material in said enlarged chamber for controlling said withdrawing means.

6. A digesting apparatus comprising in combination an elongated substantially horizontal vessel formed with an enlarged chamber communicating with the upper portion thereof, means for introducing material to be digested into said vessel, means for withdrawing the digested material from said vessel and means responsive to the level of the material within said enlarged chamber for controlling said material introducing and material withdrawing means.

7. A digesting apparatus comprising in combination an elongated substantially horizontal vessel, a cylinder positioned therein and provided with perforations, means for rotating said cylinder, means for introducing-material to be digested into said cylinder, means for introducing digesting liquor into said vessel, heat ex changingmeans, means for continuously withdrawing liquor from the digesting vessel, means for passing withdrawn liquor through said heat exchanging means, and means for reintroducing it into said vessel.

8. A digesting apparatus as in claim 7 wherein said liquor withdrawing means communicates with said vessel near its outlet end.

9. A digesting apparatus as in claim 7 where in communicating means are provided between said reintroducing means and said digesting liquor introducing means, whereby a portion of the heated withdrawn liquor may be admixed with the fresh incoming liquor.

10. A digesting apparatus as in claim 7 provided with means to supply heat to said heat exchanging means, and means responsive to the temperature within said vessel for controlling said heat supplying means.

11. A process of digesting cellulose bearing material with digesting liquor in a digesting zone including the step of controlling the withdrawal of the digested material in response to the level of material within said zone.

12. A process of digesting cellulose bearing material with digesting liquor in a digesting zone including the steps of continuously introducing the material to be digested into the digesting zone and controlling the rate of introduction in response to the level of material within said zone.

13. A continuous process of digesting cellulose bearing material in a digesting zone including the steps of continuously introducing material to be digested and digesting liquor into said zone, continuously withdrawing digested material from said zone, and controlling the rates of introduction of the material introduced and the digesting liquor and the rate of withdrawing the digested material in response to the level of the material within said zone.

14. A continuous process of digesting cellulose bearing material in a digesting zone including the steps of introducing material to be digested and fresh digesting liquor into said zone,

withdrawing a portion of the digesting liquor from said zone, heating the withdrawn liquor and admixing it with the fresh liquor being introduced in suflicient quantity to bring the temperature of mixture to a predetermined point.

15. A digesting apparatus as in claim 5, wherein said withdrawing means includes a volumetric valve.

16. A process of digesting cellulose bearing material in a digesting zone including the step of withdrawing digested material from said zone at a rate which is a function of the level of the material within said zone.

1'7. A digesting apparatus comprising in combination an elongated digesting vessel provided with an enlarged chamber communicating therewith, an inlet for'said vessel, said inlet being formed with a restriction and having opposite tapered walls extending from said restriction whereby a converging-diverging passageway is formed, a hopper for the material to be digested communicating with said passageway, a chemical solution feeding means adapted to inject a solution into said hopper, a reciprocating plunger for compacting material from said hopper through said inlet into the digesting vessel, a cylinder positioned within said vessel, said cylinder being provided with perforations, means for rotating said cylinder, means for introducing digesting liquor into said vessel, means for continuously withdrawing a portion of the digesting liquor, means forheating the withdrawn liquor and means for reintroducing the heated liquor into said vessel.

18. A continuous digesting apparatus including in combination a vessel, an unobstructed elongated container positioned within said vessel, means for rotating said container, means for introducing the material to be digested into said container and means for withdrawing di"! gested material from said container.

19. A continuous apparatus including in combination a vessel, an unobstructed elongated container positioned within said vessel, means for rotating said container, means for introducing the material to be digested into said container and means for withdrawing digested maternal from said container and means synchronizing said introducing means and said withdrawal means.

20. A digesting apparatus comprising in combination an elongated substantially horizontal vessel formed with an enlarged chamber communicating with the upper portion thereof, means for introducing material to be digested into said vessel, means for withdrawing the digested material from said vessel, and means responsive to the level of the material within said enlarged chamber for controlling said material introducing and material withdrawing means.

21. A digesting apparatus comprising in com-- bination an elongated substantially horizontal vessel having a dome, a rotatable container in the vessel and means for introducing material to be digested and withdrawal means for discharging the digested material, driving connections for rotating the cylinder positioned Within and beneath the dome and means for controlling the supply and discharge of material to and from the digestion vessel.

22. A digesting apparatus including in combination a digesting vessel, an unobstructed elongated container positioned within said vessel, means for rotating said container, means for introducing the material to be digested into said container and means for withdrawing digested material from said container and means synchronizing said introducing means and said withdrawal means.

23. A digesting apparatus including in combination a digesting vessel, an elongated container positioned within said vessel, .means forintroducing a chemical solution to said elongated container and a vapor chamber having vapor relief means above said digesting vessel.

24. An apparatus for digesting fibrous or cellular material comprising a rotating digesting container, a vapor dome communicating with said container, an inlet adapted to compact material during its passage through the inlet to form a closure plug for said container, means for compacting material through said inlet and means for discharging digested material.

' JOAQUIN JULIO DE LA ROZA, SR. 

